1. Technical Field
The present invention relates generally to the discovery and production of hydrocarbons, and more particularly, to the monitoring of downhole formation properties during drilling and production.
2. Related Art
Wells for the production of hydrocarbons such as oil and natural gas must be carefully monitored to prevent catastrophic mishaps that are not only potentially dangerous but also that have severe environmental impacts. In general, the control of the production of oil and gas wells includes many competing issues and interests including economic efficiency, recapture of investment, safety and environmental preservation.
On one hand, to drill and establish a working well at a drill site involves significant cost. Given that many xe2x80x9cdry holesxe2x80x9d are dug, the wells that produce must pay for the exploration and digging costs for the dry holes and the producing wells. Accordingly, there is a strong desire to produce at a maximum rate to recoup investment costs.
On the other hand, the production of a producing well must be monitored and controlled to maximize the production over time. Production levels depend on reservoir formation characteristics such as pressure, porosity, permeability, temperature and physical layout of the reservoir and also the nature of the hydrocarbon (or other material) extracted from the formation. Additional characteristics of a producing formation must also be considered, such characteristics include the oil/water interface and the oil/gas interface, among others.
Producing hydrocarbons too quickly from one well in a producing formation relative to other wells in the producing formation (of a single reservoir) may result in stranding hydrocarbons in the formation. For example, improper production may separate an oil pool into multiple portions. In such cases, additional wells must be drilled to produce the oil from the separate pools. Unfortunately, either legal restrictions or economic considerations may not allow another well to be dug thereby stranding the pool of oil and, economically wasting its potential for revenue.
Besides monitoring certain field and production parameters to prevent economic waste of an oilfield, an oilfield""s production efficiencies may be maximized by monitoring the production parameters of multiple wells for a given field. For example, if field pressure is dropping for one well in an oil field more quickly than for other wells, the production rate of that one well might be reduced. Alternatively, the production rate of the other wells might be increased. The manner of controlling production rates for different wells for one field is generally known. At issue, however, is obtaining the oil field parameters while the well is being formed and also while it is producing.
In general, control of production of oil wells is a significant concern in the petroleum industry due to the enormous expense involved. As drilling techniques become more sophisticated, monitoring and controlling production even from a specified zone or depth within a zone is an important part of modern production processes.
Consequently, sophisticated computerized controllers have been positioned at the surface of production wells for control of uphole and downhole devices such as motor valves and hydromechanical safety valves. Typically, microprocessor (localized) control systems are used to control production from the zones of a well. For example, these controllers are used to actuate sliding sleeves or packers by the transmission of a command from the surface to downhole electronics (e.g., microprocessor controllers) or even to electro-mechanical control devices placed downhole.
While it is recognized that producing wells will have increased production efficiencies and lower operating costs if surface computer based controllers or downhole microprocessor based controllers are used, their ability to control production from wells and from the zones served by multilateral wells is limited to the ability to obtain and to assimilate the oilfield parameters. For example, there is a great need for real-time oilfield parameters while an oil well is producing. Unfortunately, current systems for reliably providing real-time oilfield parameters during production are not readily available.
Moreover, many prior art systems generally require a surface platform at each well for monitoring and controlling the production at a well. The associated equipment, however, is expensive. The combined costs of the equipment and the surface platform often discourage oil field producers from installing a system to monitor and control production properly. Additionally, current technologies for reliably producing real time data do not exist. Often, production of a well must be interrupted so that a tool may be deployed into the well to take the desired measurements. Accordingly, the data obtained is expensive in that it has high opportunity costs because of the cessation of production. It also suffers from the fact that the data is not true real-time data.
Some prior art systems measure the electrical resistivity of the ground in a known manner to estimate the characteristics of the reservoir. Because the resistivity of hydrocarbons is higher than water, the measured resistivity in various locations can be of assistance in mapping out the reservoir. For example, the resistivity of hydrocarbons to water is about 100 to 1 because the formation water contains salt and, generally, is much more conductive.
Systems that map out reservoir parameters by measuring resistivity of the reservoir for a given location are not always reliable, however, because they depend upon the assumption that any present water has a salinity level that renders it more conductive that the hydrocarbons. In those situations where the salinity of the water is low, systems that measure resistivity are not as reliable.
Some prior art systems for measuring resistivity include placing an antenna within the ground for generating relatively high power signals that are transmitted through the formation to antennas at the earth surface. The amount of the received current serves to provide an indication of ground resistivity and therefore a suggestion of the formation characteristics in the path formed from the transmitting to the receiving antennas.
Other prior art systems include placing a sensor at the bottom of the well in which the sensor is electrically connected through cabling to equipment on the surface. For example, a pressure sensor is placed within the well at the bottom to attempt to measure reservoir pressure. One shortfall of this approach, however, is that the sensor does not read reservoir pressure that is unaffected by drilling equipment and formations since the sensor is placed within the well itself.
Other prior art systems include hardwired sensors placed next to or within the well casing in an attempt to reduce the effect that the well equipment has on the reservoir pressure. While such systems perhaps provide better pressure information than those in which the sensor is placed within the well itself, they still do not provide accurate pressure information that is unaffected by the well or its equipment.
Alternatives to the above systems include sensors deployed temporarily in a wireline tool system. In some prior art systems, a wireline tool is lowered to a specified location (depth), secured, and deploys a probe into engagement with the formation to obtain samples from which formation parameters may be estimated. One problem with using such wireline tools, however, is that drilling and/or production must be stopped while the wireline tool is deployed and while samples are being taken or while tests are being performed. While such wireline tools provide valuable information, significant expense results from xe2x80x9ctrippingxe2x80x9d the well, if during drilling, or stopping production.
Thus, there exists a need in the art for a reservoir management system that efficiently senses reservoir formation parameters so that the reservoir may be drilled and produced in a controlled manner that avoids waste of the hydrocarbon resources or other resources produced from it.
To overcome the shortcomings of the prior systems and their operations, the present invention contemplates a reservoir management system including a centralized control center that communicates with a plurality of remote sensing units that are deployed in the subsurface formations of interest by way of communication circuitry located near the earth surface at the well site. According to specific implementations, the deployed remote sensing units provide formation information either to a measurement while drilling tool (MWD) or to a wireline tool. The well control unit is coupled either to a least one antenna or to a downhole data acquisition system that includes an antenna for communicating with the remote sensing units.
Because the remote sensing units are already deployed, the downtime associated with gathering remote sensing unit information via a wireline tool is minimized. Because the invention may be implemented through MWD tool, there is no downtime associated with gathering remote sensing unit information during drilling. Accordingly, formation information may be obtained more efficiently, and more frequently thereby assisting in the efficient depletion of the reservoir.
In one version of the described embodiment, a central control center communicates with a plurality of well control units deployed at each well for which remote sensing units have been deployed. Some wells include a drilling tool that is in communication with at least one remote sensing unit while other wells include a wireline tool that is communication with at least one remote sensing unit. Other wells include permanently installed downhole electronics and antennas for communicating with the remote sensing units. Each of the wells that have remote sensing units deployed therein include circuitry for receiving formation data received from the remote sensing units. In some embodiments, a well control unit serves to transpond the formation data to the central control unit. In other embodiments, an oilfield service vehicle includes transceiver circuitry for transmitting the formation data to the central control system. In an alternate embodiment, a surface unit, by way of example, a well control unit merely stores the formation data until the data is collected through a conventional method.
Some of the methods for producing the formation data to the central control center for analysis include conventional wireline links such as public switched telephone networks, computer data networks, cellular communication networks, satellite based cellular communication networks, and other radio based communication systems. Other methods include physical transportation of the formation data in a stored medium.
The central control center receives the formation data and analyzes the formation data for a plurality of wells to determine depletion rates for each of the wells so that the field may be depleted in an economic and efficient manner. In the preferred embodiment, the central control center generates control commands to the well control units. Responsive thereto, the well control units modify production according to the received control commands. Additionally, the well control units, wherever installed, continue to periodically produce formation data to the central control center so that local depletion rates may be modified if necessary.
An antenna system is utilized to effectively deliver power to the remote sensing unit and to allow a communication link to be established with the remote sensing unit. While the antenna system may be implemented in many different configurations, each configuration of the preferred embodiment includes at least two antenna coil sections that are formed to conduct current in opposite directions. The spacing between the at least two antenna coil sections is one that most likely will equal the expected distance between an axis of the casing joint and the remote sensing unit. In the described embodiment, the coil sections define a plane that is perpendicular to the axis defined by the casing section and, therefore, create a dipole that is parallel to the axis defined by the casing section. This particular arrangement is made to result in a dipole that is substantially perpendicular to the dipole of the remote sensing unit antenna. For each of the preferred embodiments, the antenna coil sections are wound about a ferrite core to improve the strength of the electromagnetic radiation emitted therefrom.